The conventional way of fastening the cover with the shell of a box, chest, etc. involves the use of the hooked body of a locking device in such a manner that the hooked body traverses the corresponding outer sides of the cover and the shell. Another conventional way involves the use of an elongated locking device which consists of an elongated main body, a pair of lock retainers, a pair of retaining members, a pair of press buttons, and a combination lock. The main body is fastened with the shell. The combination lock is disposed in the center of the main body. The lock retainers are fastened pivotally with both ends of the main body such that they are corresponding in location to a pair of lock hooks. The retaining members are respectively disposed between the lock retainers and the combination lock. The press buttons are disposed on the lock retainers. When the lock is in a releasing state, the user may press the press buttons to force the lock retainers to disengage the lock hooks, thereby enabling the cover to be separated from the shell. When the user turns the combination lock to cause the lock to remain in the locking state, the two retaining members are forced by the combination lock to remain stationary such that the stationary retaining members keep the press buttons in the stationary state. As a result, the cover and the shell can not be separated from each other.
Such a prior art locking device as described above is defective in design in that it is rather complicated in construction, and that the retaining members must be located with precision between the combination locks and the press buttons, and further that it can not be assembled easily, and still further that it fails easily.